Hi! Very cool game so far! I played the 3 maps of the demo campaign.
Here is some feedback for you:
1) My biggest complaint: I don't think I should lose, just because the enemy has more land than me. It's a bit frustrating. I lost multiple times like that, although I knew I could beat them and push them back with more time. In my opinion I should only lose, when they take my castle.
2) I think the bowman should be able to shoot in melee range, without getting attacked back (but maybe you disagree :D)
3) The tutorial was a bit buggy. I didn't have enough gold to buy the unit, that the tutorial wanted me to buy. Also please don't let the enemy spawn so many units in the tutorial. Just let the player win.
4) The enemies are a bit dumb sometimes. They probably shouldn't walk into water, when there are enemies(me) nearby.
All in all very cool game already! Keep it up :)